This application claims the priority of German Patent Document 199 57 508.8, filed in Germany, Nov. 30, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device and process for joining fitting parts on hollow profiles fluid high internal pressure.
A device of this general type is known from German Patent Document 37 16 986 A1 (corresponding to U.S. Pat. No. 5,054,756). The hollow profile is expanded plastically at the joining location by means of fluid high internal pressure. The more solid fitting part is expanded simultaneously within the elastic limits. Following high pressure release, the fitting part springs back at the internal diameter of its passage opening, whereas the hollow profile remains in its plasticized state. These physical features make it possible to achieve a very high, virtually undetachable press-fit joint between the fitting part and the hollow profile. In operation, i.e., at an existing high internal pressure, the expanding lance, which is used for this purpose and described there, is highly subjected to extreme tensile stress so that constructive measures, such as for example an increase in the ratio of the lance diameter to the diameter of the axial borehole, which runs in the expanding lance and guides the pressure fluid, must be taken in order to prevent the expanding lance from tearing and to guarantee in this manner a reliable process for joining the fitting parts on the hollow profiles. Nevertheless, the lance is subject to relatively high wear due to the high tensile stress or the mechanical stress alternating between stress and relief in the course of the operating life of the expanding lance. For this reason after a specific period of use it is necessary to repair the lance or make an expensive replacement with an identical new lance. Furthermore, hollow profiles with a small outer diameter, i.e., less than 16 mm, cannot be reliably joined by the customary method, since in the course of the process the use of correspondingly thin (less than 10 mm outer diameter) expanding lances results in the lance snapping after just a few expansion operations (called xe2x80x9cshotsxe2x80x9d in the technical jargon due to their speed). This state in turn results inevitably in a production standstill and a rejected part.
An object of the invention is to improve a device of this class to the effect that the joining of fitting parts on hollow profiles by means of partial high internal pressure deformation is also possible and reliable with an expanding lance even when the hollow profiles exhibit small outer diameters.
This object is achieved by the invention by providing a device for joining fitting parts, provided with a device for joining fitting parts, provided with a passage opening, on a hollow profile through partial expansion of the hollow profile at a location of the fitting parts, slid on with the passage opening, by means of fluid high internal pressure, said device comprising an expanding lance, which can be slid into the hollow profile and exhibits an axial borehole for the purpose of guiding the pressure fluid, said axial borehole being connected, first of all, to a fluid high pressure generating system and secondly exhibiting a cross channel with an outlet for the pressure fluid in a direction of the hollow profile location to be expanded, whereby the shell surface of the expanding lance exhibits sealing elements that are spaced apart and that define an outlet so as to seal axially on both sides against high pressure, wherein the expanding lance comprises two separate, aligned components, of which at least one bears the axial borehole, which axial borehole empties freely on an end face near an outlet of said at least one component, end faces of the oblong components that face each other forming a cross channel for the axial borehole of the expanding lance, and wherein the device includes a drive unit, operable to drive the two components into the hollow profile end, facing the respective component, and are supported on the end side during the expansion phase.
Thanks to the invention, tensile stress of the expanding lance is avoided. The two components of the lance are subjected only to pressure so that the lance is prevented from tearing. Since the stability of the lance with respect to an adequately strong xe2x80x9cwall thicknessxe2x80x9d is no longer important due to the solution of the invention, the outer diameter of the expanding lance and the axial borehole can be dimensioned very small and, nevertheless, work reliably. In this manner fitting parts can also be joined in the desired manner on hollow profiles with small outer diameter by means of partial high internal pressure deformation with the pressure fluid-guiding expanding lance.
With the device of the invention, joining is done preferably sequentially. This means that each individual joint along the hollow profile is approached in succession by displacing the expanding lance inside the hollow profile. For few fitting parts this type of joining does exhibit negligibly higher timing than the joining of parts in a shot. Furthermore, it has been demonstrated to be advantageous for the process if owing to the small volume of fluid, required for sequential joining, the time for building up the high fluid pressure is also very short. Furthermore, the assembly of the expanding lance is significantly simplified over the conventional one.
Hence, it is not necessary to have a leakage borehole for draining the fluid volume from the hollow profile in the direction of the outside. Said volume of fluid creeps past the sealing arrangement, sealing both sides of the expansion point in the axial direction, and into the pressure-free, adjoining annular slit. Or when the previous seal fails, there is the risk of an expansion between the fitting parts, since in the case of a leak, the pressure fluidxe2x80x94when the seal carrier for passage of an adequately large quantity of fluid volume has been suitably designedxe2x80x94can flow out unimpeded.
In addition, objects achieved in this respect by means of the invention are that the design of the high pressure unit can be simpler, since it is no longer necessary that it automatically recognize a drop in pressure. In addition, there is no need for spacer sleeves and positioning stops. Furthermore, it is significantly simpler to compensate for the manufacturing-induced concentricity error at the internal diameter of the hollow profile with the design of the expanding lance, since only the single expansion area of the expanding lance must be designed in accordance with the error tolerance. This feature contributes to the simplified design of the expanding lance and to the use of less precisely machined and, therefore, less expensive hollow profiles.
Another important advantage of the expanding lance having two parts is that the two components can be spaced axially apart at variable distances so that with only one sealing arrangement at the hollow profile, expansions of varying length can be formed. Furthermore, there is the possibility of tailoring individually the fluid pressure height to the diverse expansion points and their desired final shape.
It is also contemplated by the invention to provide one or both components of the lance with other cross boreholes so that several points on the hollow profile can be expandedxe2x80x94as usualxe2x80x94simultaneously in one shot. In so doing, the customary lance head can be dispensed with. However, the aforementioned advantages of sequential joining also drop away.
Advantageous designs of the invention are disclosed below and in the claims.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.